Examples of the conventionally-known vehicles include ones which include a cast (cast-molded) subframe provided on a vehicle body frame and which include suspension arms connected to left and right end portions of the subframe so that left and right suspensions are supported respectively by the left and right suspension arms.
A plurality of ribs is provided on the subframe so that a sufficient rigidity and strength of the subframe can be secured by the ribs (see, for example, Patent Literature 1).
With the subframe disclosed in Patent Literature 1, it is required to determine molded directions (orientations) of the plurality of ribs in such a manner as to secure a sufficient rigidity and strength of the subframe.
Further, in casting the subframe, it is required to smoothly direct molten metal into a cavity of a casting mold. As a means for directing the molten metal into the casting mold cavity, it is conceivable to conform or match the orientations of the plurality of ribs with the flowing direction of the ribs. However , it is difficult to determine the orientations of the plurality of ribs so as to secure a sufficient rigidity and strength of the subframe and match the molten metal flowing direction. For example, if the orientations of the plurality of ribs are determined so as to smooth the molten metal flows, it tends to be difficult to secure a sufficient rigidity and strength of the subframe by means of the plurality of ribs.
Thus, if the molten metal flows are to be smoothed by the plurality of ribs, it is necessary to increase a wall thickness of the subframe to thereby secure a sufficient rigidity and strength of the subframe, which cannot meet a demand for minimizing an increase of the weight of the subframe.